To produce an image of an environment of a vehicle for a driver-assistance system, a system based on LIDAR (light detection and ranging) may be used in addition to other systems. In a LIDAR system, the environment is illuminated line-by-line by a point of light from a pulsed laser light source. A contour of the environment is determined from the amplitude or the intensity of the reflected and backscattered light. In addition, the distance to objects is determined from the propagation time of the light pulses, so that a three-dimensional image of the environment is able to be produced overall, which may be evaluated with the aid of image-processing software. The line by line scanning must take place so rapidly that a reaction time suitable for operating a vehicle is able to be realized. Micromechanical mirrors, as they are used in digital projection devices as well, constitute a suitable system for this purpose.
According to the related art, micromechanical mirrors are patterned out of a silicon wafer in a CMOS-compatible process. The created mirror surface can be deflected electrostatically or electromagnetically.
A suitable micromechanical mirror is described in DE 198 57 946 C1. DE 198 57 946 C1 describes a device in which an oscillating micro-mirror has a self-supporting mirror surface, which is at least regionally connected to a carrier element surrounding the mirror surface, via at least one torsion axis formed by a torsion beam mounted on the mirror surface. A bending beam is situated at least between a torsion beam and the carrier element, which bending beam executes a flexural vibration that induces a torsional oscillation of the minor surface about the torsion axis. The amplitude of the oscillation of the mirror surface is especially large if the device is oscillating in resonance. According to the related art, such devices are therefore operated in resonance. It is known to use a laser adjustment to bring devices of this type to identical resonant frequencies in order to compensate for tolerances stemming from the manufacturing process.
Disadvantageous in the devices and methods according to the related art is that the maximum deflection angle of the laser radiation is fixedly specified in the vertical and horizontal direction. It is therefore necessary to use the same angular range for detection tasks in the near field and the distant field. If a smaller detection field is required in the distant field, for example, then the resolution of the device—evaluated in pixels—drops in the small detection field given a constant angular resolution.